Thursday, July 9, 2015

Dear(s)[something rudimentary for Engineers and something of valuable information for those with no Engineering background.Here is something circulated to my small group on 21st Dec 2008 and posted on my blog now]

Recently, we discussed internally a claim on transformer which threw up some interesting and some basic doubts.For those of us with no Engg.background, many timesit is a struggle to understand rudimentary elements also.Arising out of experience in that meeting, here is some on Transformer for understanding which something on Electricity is quintessential.

Electricity completely surrounds us -- For most of us, modern life would be impossible without it.Batteries, fuel cells and solar cells all produce something called direct current (DC). The positive and negative terminals of a battery are always, respectively, positive and negative. Current always flows in the same direction between those two terminals.The power that comes from a power plant, on the other hand, is called alternating current (AC). The direction of the current reverses, or alternates, 60 times per second (in the U.S.) or 50 times per second (in Europe, for example). The power that is available at a wall socket in the United States is 120-volt, 60-cycle AC power.Electricity in India is 240 Volts, alternating at 50 cycles per second

Electricity is a form of energy. Electricity is the flow of electrons. All matter is made up of atoms, and an atom has a centre, called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons. The negative charge of an electron is equal to the positive charge of a proton, and the number of electrons in an atom is usually equal to the number of protons. When the balancing force between protons and electrons is upset by an outside force, an atom may gain or lose an electron. When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current.

Electricity is a basic part of nature and it is one of our most widely used forms of energy. We get electricity, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work. Before electricity generation began slightly over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by wood-burning or coal-burning stoves. Beginning with Benjamin Franklin's experiment with a kite one stormy night in Philadelphia, the principles of electricity gradually became understood. In the mid-1800s, everyone's life changed with the invention of the electric light bulb. Prior to 1879, electricity had been used in arc lights for outdoor lighting. The lightbulb's invention used electricity to bring indoor lighting to our homes.

Electricity is generated by usage of many equipments.An electric generator is a device for converting mechanical energy into electrical energy. The process is based on the relationship between magnetism and electricity. When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire. The large generators used by the electric utility industry have a stationary conductor. A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a long, continuous piece of wire. When the magnet rotates, it induces a small electric current in each section of wire as it passes. Each section of wire constitutes a small, separate electric conductor. All the small currents of individual sections add up to one current of considerable size. This current is what is used for electric power.

An electric utility power station uses eithera turbine, engine, water wheel, or other similar machine to drive an electric generator or a device that converts mechanical or chemical energy to electricity. Steam turbines, internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity. Electricity is measured in units of power called watts. It was named to honour James Watt, the inventor of the steam engine. One watt is a very small amount of power. It would require nearly 750 watts to equal one horsepower. The amount of electricity a power plant generates or a customer uses over a period of time is measured in kilowatt-hours (kWh). Kilowatt-hours are determined by multiplying the number of KW's required by the number of hours of use. For example, if you use a 40-watt light bulb 5 hours a day, you have used 200 watts of power, or .2 kilowatt-hours of electrical energy.

NOW COMES TRANSMISSION- i.e.,sending electricity over long distances, George Westinghouse developed a device called a transformer.

The transformer allowselectricity to be efficiently transmitted over long distances. This made it possible to supply electricity to homes and businesses located far from the electric generating plant.

The electricity soproduced by a generating plant travels along cables to a transformer, which changes electricity from low voltage to high voltage. Electricity can be moved long distances more efficiently using high voltage. Transmission lines are used to carry the electricity to a substation. Substations have transformers that change the high voltage electricity into lower voltage electricity. From the substation, distribution lines carry the electricity to homes, offices and factories, which require low voltage electricity.As electricity flows down a metal wire, the electrons that carry its energy jiggle through the metal structure, bashing and crashing about and generally wasting energy like unruly schoolchildren running down a corridor. That's why wires get hot when electricity flows through them (something that's very useful in electric toasters). It turns out that the higher the voltage electricity you use, and the lower the current, the less energy is wasted in this way. So the electricity that comes from power plants is sent down the wires at extremely high voltages to save energy.

An electrical transformer changes the voltage of the electricity. It can only work using AC (alternating current). It transforms electricity at one voltage into electricity at another voltage. Household gadgets need electrical transformers because the mains electricity comes in at 240 Volts; that's enough to kill you. And what's more the electronic circuits that most modern machines use would burn up in an instant if they were connected to electricity at this voltage.

To do its magic on the high voltage and change it to low voltage the electrical transformer uses two rather intriguing and important phenomena. Firstly whenever an electric current flows, there is magnetism around it. Secondly whenever a magnetic field changes (by moving or by changing strength) a voltage is made. If there's a wire close by when this happens then a current will flow in the wire as the magnetism changes. The electrical transformer takes in high voltage electricity and lets it run through lots of coils wound around an iron core. Because the current is alternating the magnetism in the core is also alternating. Also round the core is an output wire with less coils. The changing magnetism generates a current in the wire and less coils means less voltage. So the voltage is 'stepped-down'.

Unfortunately this transformation takes some energy so you get slightly less energy out of the transformer than you put in, but the loss is usually only small.The electricity in the transformer will not flow between the coils as there are layers of insulating materials

There are more terms like Amperes, Watts, Volts, Joulesetc., which could be far more complex than they sound to be.Using a water anaolgy, volts would be the water pressure, current (amps) would be the velocity of the water, resistance would be the size of pipe (ohms), and watts would be the mass flow rate.This is a very crude analogy.